Your pieces of cannas can survive even this. i am no way an expert, but i have 3 ideas that may work.
1 - put those pieces you have in slightly damp peat moss in a small cardboard box and put them in the coolest dark spot in your house. The hope here is to imitate underground conditions in a warm climate for replanting in Spring. I've had fat big-eyed rhizomes with roots ready to plant in Spring this way.
2 - if you have a full sun southern exposure window: half submerge a piece in a dish of water, changed occassionaly. I have grown blooming cannas in water this way if warm & bright enough.
3-google both Karchesky Cannas & "storing cannas"...
good luck! marea